This invention relates generally to sprue gated injection molding apparatus for five layer molding and more particularly to such apparatus having two melt passages extending from a common melt source with one of the melt passages having a control valve to control melt flow to a central melt channel in each heated nozzle.
Multi-cavity injection molding apparatus for making five layered protective containers for food or preforms or parisons for beverage bottles are known. Two layers of a barrier material such as ethylene vinyl alcohol copolymer (EVOH) or nylon are molded between two outer layers and a central layer of a polyethylene terephthalate (PET) type material. For instance, U.S. Pat. No. 4,717,324 to Schad et al. which issued Jan. 5, 1988 shows apparatus for sequentially injecting first the PET, then the barrier material and finally the PET again through two different melt channels. While this is satisfactory for some applications, sequential molding has the disadvantage of a relatively lengthy cycle time.
As seen in U.S. Pat. Nos. 4,990,301 to Krishnakumar et al. which issued Feb. 5, 1991, U.S. Pat. No. 5,131,830 to Orimoto et al. which issued Jul. 21, 1992, and U.S. Pat. No. 5,141,695 to Nakamura which issued Aug. 25, 1992 injection molding apparatus is also known to simultaneously inject multi-layered products, but this apparatus has the disadvantage of requiring a separate melt source and a separate valve for each melt passage.
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing multi-cavity injection molding apparatus for five layer molding having only two melt sources and only one control valve.
To this end, in one of its aspects, the invention provides multi-cavity sprue gated injection molding apparatus for five layer molding having one or more melt distribution manifolds with a front face and a plurality of heated nozzles mounted in a mold. Each heated nozzle has a rear end abutting against the melt distribution manifold and a front end adjacent a gate leading to a cavity in the mold. Each heated nozzle has first, second and third melt channels extending therethrough from the rear end to the front end. A first melt passage for conveying melt from a first melt source branches in the melt distribution manifold and extends through the first melt channel in each heated nozzle to the gate. A second melt passage for conveying melt from a second melt source branches in the melt distribution manifold and extends through the second melt channel in each heated nozzle to the gate. A third melt passage for conveying melt from the first melt source branches in the melt distribution manifold and extends through the third melt channel in each heated nozzle to the gate. The first melt passage has a valve therein upstream of the branching to control melt flow to the first melt channel in each heated nozzle according to a predetermined cycle.
In another of its aspects, the invention provides a method of continuously injection molding five layer products in a multi-cavity injection molding apparatus having a melt distribution manifold and a plurality of heated nozzles mounted in a mold. Each heated nozzle has a rear end abutting against the melt distribution manifold and a front end adjacent a gate leading to a cavity in the mold. Each heated nozzle has a central melt channel extending therethrough from the rear end to the front end, an inner annular melt channel extending around the central melt channel to the front end and an outer annular melt channel extending around the inner annular melt channel to the front end. A first melt passage extending from a common inlet in the melt distribution manifold and having actuated valve means therein branches in the melt distribution manifold and extends through the central melt channel in each heated nozzle to the gate. A second melt passage branches in the melt distribution manifold and extends through the inner annular melt channel in each heated nozzle to the gate. A third melt passage also extending from the common inlet in the melt distribution manifold branches in the melt distribution manifold and extends through the outer annular melt channel in each heated nozzle to the gate. The method comprises the steps of, with the valve means in the first melt passage in the closed position, injecting a first molten material from a first melt source through the common inlet to the first and third melt passages, whereby the first molten material flows in the third melt passage through the outer annular channel in each heated nozzle and the aligned gated into the cavities. After a predetermined quantity of the first molten material has been injected into the cavities, simultaneously injecting a second molten material from a second melt source into the cavities through the second melt passage, whereby the second molten material flows through the inner annular melt channel in each heated nozzle and the aligned gate and splits the first molten material flowing from the outer annular channel in each heated nozzle to form two outer layers of the first material in each of the cavities. Then after flow of the second molten material into the cavities has been established, actuating the valve means in the first melt passage to the open position to simultaneously inject first molten material from the first melt source into the cavities through the first melt passage, whereby the first molten material flows through the central melt channel in each heated nozzle and the aligned gate and splits the second molten material flowing from the inner annular channel in each heated nozzle to form a central layer of the first material between two intermediate layers of the second material in each of the cavities. When the cavities are nearly full, the injection of the second material through the second melt passage is discontinued, while the injection of the first material is continued until the cavities are full. After a cooling period, the mold is opened to eject the molded products. Finally, the mold is closed after ejection of the molded products.
Further objects and advantages of the invention will appear from the following description taken together with the accompanying drawings.